The invention relates to an article of footwear with a sole that includes a stability element to control, in a preselected manner, the rotation of the forefoot area with respect to the rearfoot area of the article of footwear.
The processes in the human foot during walking or running are enormously complex. Between the first contact of the heel and the push-off with the toes, a number of different movements take place throughout the entire foot. During these movements, various parts of the foot move or turn with respect to each other.
It is an objective in the construction of xe2x80x9cnormalxe2x80x9d footwear, to obstruct these natural movements, such as they occur in barefoot running, as little as possible and to support the foot only where it is necessary for the intended use of the footwear. In other words, the objective is to simulate walking or running barefoot.
In contrast thereto, it is an objective of orthopedic footwear to correct malpositions or orthopedic deformities of the foot, for example, by reinforcing the material in certain parts of the sole to provide additional support for the foot. The present invention, however, focuses on the construction of footwear for xe2x80x9cnormalxe2x80x9d feet, though it may be useful in other applications.
In this context, it was already realized in the past that the classical outsole, which extends over the entire article of footwear, does not meet the above mentioned requirements. In particular, rotations of the forefoot area around the longitudinal axis of the foot with respect to the rearfoot area (referred to in physics as torsional movements) are, at the least, considerably hindered by a homogeneously formed, continuous outsole or arrangement of soles.
To overcome these difficulties, stability elements were developed which supply separate parts of the sole with a controlled rotational flexibility, and which define by their form and their material the resistance of the sole against such twisting movements.
One example of a known stability element is disclosed in U.S. Pat. No. 5,647,145. The footwear sole construction described in this prior art approach complements and augments the natural flexing actions of the muscles of the heel, metatarsals and toes of the foot. To meet this objective, the sole comprises a base of resiliently compressible material, a plurality of forward support pads supporting the toes, a plurality of rearward support lands supporting the metatarsals, a heel member supporting and protecting the heel of the wearer""s foot, and a central heel fork which overlays and is applied to the heel member. At heel strike, the heel fork tends to help stabilize and hold or reduce the rearfoot from over-supination or over-pronation by guiding and stabilizing the heel bone.
Another embodiment of a known stability element (which is similar to the above described heel fork) is shown and discussed in conjunction with FIG. 14 of the present application. The stability element 10xe2x80x2 shown in FIG. 14 is shaped like a bar, a cross, or a V, and starts at the rearfoot area 2xe2x80x2 of the sole and terminates in the midfoot area of the sole.
These known stability elements are capable of providing some stability to the various parts of the foot through their rigidity, however, an important disadvantage is that they provide insufficient joint support for the longitudinal and lateral arch of the foot. Compared to an ordinary continuous sole molded to the contour of the foot, stability is considerably reduced.
Furthermore, the arrangement of layers of foamed materials typically used in the forefoot area is relatively yielding so that due to the high impact forces that occur during running the sole yields on the medial or lateral side, and the foot rotates in response thereto by a few degrees to the inside or the outside, particularly if the wearer""s foot anatomy tends to support such rotational movements. These rotational movements are known in the art as pronation and supination, respectively, and lead to premature fatigue of the joints of the foot and knee, and sometimes to injuries.
Additionally, a sole with a soft or yielding forefoot area leads to a loss of energy. The deformation of the sole during the push-off phase of the step is not elastic, therefore, the energy used for the preceding deformation of the sole cannot be regained.
It is an objective of the present invention to provide an article of footwear which controls, in a preselected manner, the rotation of the forefoot area with respect to the rearfoot area and at the same time supports the forefoot area to avoid excessive pronation or supination, thereby reducing and/or preventing premature fatigue or injuries to the wearer.
According to another aspect of the invention, the footwear sole should store any energy applied during the landing phase and supply it to the course of movements at the correct time during the push-off phase of the foot.
In one aspect, the invention relates to an article of footwear including a rearfoot portion, a forefoot portion, and a sole with a stability element. The stability element extends from the rearfoot portion into the forefoot portion, and is constructed of a material and configured for controlling, in a preselected manner, the rotation of the forefoot portion of the shoe around the longitudinal axis with respect to the rearfoot portion.
The stability element can extend substantially along the medial side of the shoe, or substantially along the lateral side. The stability element can include a forefoot area including material properties for reducing pronation or supination of the wearer""s foot.
According to another embodiment, in this case for pronation control, metatarsals one and/or two of the wearer""s foot are supported, preferably together with phalanges one and/or two. In the case of supination control, metatarsals five and preferably four are supported, preferably together with phalanges five and/or four.
Due to the extension of the stability element from the rearfoot portion into the forefoot portion where the metatarsals and phalanges are located, the foot is supported over its effective longitudinal length without affecting the flexibility of the footwear with respect to the twisting of the forefoot portion relative to the rearfoot portion. Excessive strain or the breaking of the longitudinal arch of the foot under high stress, for example, the landing after a leap, is effectively avoided. In addition, the stability element supports the front part of the foot in the forefoot area.
A camera using high-speed film photographed the feet of running athletes during a pronation study. The photographs show that footwear with a supported forefoot area effectively avoids the turning of the foot to the medialside. The reason is that the material properties of the stability element in the forefoot area of an article of footwear do not yield on the medial side under higher pressure. Preferred materials for the forefoot area of the stability element have a longitudinal bending strength in the range of approximately 350 N/mm2 to 600 N/mm2 and a lateral bending strength of approximately 50 N/mm2 to 200/mm2 (measured according to DIN 53452).
According to another embodiment of the invention, the stability element comprises an elastic forefoot plate, or has elastic properties in the forefoot area. During landing of the foot and the subsequent rolling of the toes, the forefoot area is elastically bent. In the subsequent course of the movement, after the rearfoot part has left the ground, the foot is stretched to push-off from the ground. At this moment, the forefoot area of the stability element springs elastically back into its original shape; thereby supporting the push-off from the ground. In this way, the energy invested for the elastic deformation of the shoe is regained and aids the continuation of the movement. The forefoot plate or area preferably shows a stiffness in the range of approximately 50 N/mm to 100 N/mm (measured according ASTM 790).
According to another embodiment, the stability element includes two parts connected in a V-like shape. This allows precise adaptation to the different forms of both the medial and the lateral side of the longitudinal arch of the foot.
The stability element can include at least one support element at its side. The lateral arch of the foot is specifically supported by the support element(s) of the stability element. The stability element can also include at least one side element which extends upwardly from the side of the stability element over the edge of the footwear. This embodiment is preferred for use in sports with a high lateral strain on the foot.
The above mentioned material properties can be obtained by manufacturing the stability element from a composite material of resin and carbon fibers.
These and other objects, along with advantages and features of the present invention herein disclosed, will become apparent through reference to the following description of embodiments of the invention, the accompanying drawings, and the claims.